Types of Casings
Artificial food casings used throughout the world in processing a great variety of meat and other food products, such as sausages of various types, cheese rolls, turkey rolls, and the like are customarily prepared from regenerated cellulose and other cellulose materials. Casings are of several different types and sizes to accomodate the different categories of food product to be prepared and are provided in supported or unsupported form, the supported casings, commonly referred to as "fibrous casings", having a fibrous support web embedded in the casing wall.
A common feature of many processed food products, particularly meat products, is that the mixture of comestible ingredients, commonly called an "emulsion", is stuffed into a casing under pressure, and processing of the food product is carried out after its encasement. The food product may also be stored and shipped while encased in the casing, though in many instances, and particularly with small sausage products such as frankfurters, the casing is removed from the food product after completion of the processing.
The designation "small size food casings" refers generally to those casings employed in the preparation of small size sausage products such as frankfurters. As the name suggests, this type of food casing is small in stuffed diameter, generally having a diameter within the range of from about 15 mm to about 40 mm, and is most usually supplied as thin-walled tubes of very great length. For convenience in handling, these casings, which may be 20 to 50 meters in length or even longer, are shirred and compressed to produce what is commonly referred to as "shirred casing sticks" of from about 20 cm to about 60 cm in length. Shirring machines and the products thereof are shown in U.S. Pat. Nos. 2,983,949 and 2,984,574 among others.
"Large size food casings", the common designation for casings used in the preparation of generally larger food products, such as salami and bologna sausages, meat loaves, cooked and smoked ham and smoked pork butts and the like, are produced in stuffed diameters sizes of from about 50 mm to about 200 mm or even larger. In general, such casings have a wall thickness about three times greater than "small size casings" wall thickness, and are usually provided with a fibrous web reinforement embedded in the wall, though they may be prepared without such supporting medium. Traditionally the large size tubular casings have been supplied to the food processor in flattened condition, cut to predetermined lengths of from about 0.6 m to about 2.2 m. Improvements in shirring and packaging techniques and increased use of automatic stuffing equipment has increased the demand for supplying large size casings of both the fibrous and the unsupported types in the form of shirred sticks containing up to about 30 m and even more of casing.
Illustrative optional minor ingredients that may be present in amounts of less than 50 (preferably less than 25) weight percent in the casing based on the total casing weight include, for example, peeling aid coatings such as carboxymethylcellulose, mineral oil and an emulsifier for small size casing or alkyl-ketene dimer for large size casing; moisture barrier coatings, such as vinylidene chloride copolymer coatings; plasticizers and softeners such as oils including animal fatty oils such as lard oil and vegetable fatty oils such as castor oil, or corn oil, soya oil, safflower oil, tung oil, or mineral oil; pigments and fillers such as titanium dioxide, and dyes such as the well-known food dyes.
Cellulosic casings are flexible, usually seamless tubing formed of regenerated cellulose, cellulose ethers and the like, and can be prepared by known processes, such as the cuprammonium process, the deacetylation of cellulose acetate, the denitration of cellulose nitrate, and preferably the viscose process. Fibers used to reinforce cellulosic tubular casings may, for example, be rice paper, hemp, rayon, flax, sisal, nylon, and polyethylene terphthalate. Tubular fibrous casings can be made by methods and apparatus described, for example, in U.S. Pat. Nos. 2,105,273; 2,144,899; 2,910,380; 3,135,613; and 3,433,663.
As is well known in the art, tubular cellulosic casings prepared by any one of the well known methods are generally treated with a polyol/as for example glycerine, as a humectant and softening or plasticizing agent, to provide resistance to drying or cracking of the casing during storage and handling prior to stuffing. The glycerine treatment is usually carried out by passing the casing while still in its gel state through an aqueous glycerine solution, after which the plasticized casing is dried to a predetermined moisture content prior to further processing or winding up on reels for interium storage. Generally, large size cellulosic casings will contain about 2% to 35% glycerine based on the weight of dry cellulose, and small size cellulosic casing contain about 9% to 17% glycerine on the same basis. However, as discussed hereinafter in greater detail, there is a trend toward lower glycerine content and greater reliance on water as a softener in cellulosic casings.